In a retail store or the like, management of commodities arranged in a shelf is necessary. For example, an inventory operation takes time and labor, and accordingly it is an operation requiring large load for a salesclerk. Conventionally, there is an inventory system which counts the number of articles using an object sensor for measuring a distance to an object and a movement mechanism for moving the object sensor. This inventory system determines actual arrangement data of objects, based on data which a distance sensor fixed to a main body moving in front of the shelf measures.
The inventory system with the configuration like this cannot detect a state of an article arranged behind an article arranged at the front, by the distance sensor. In an actual retail store or the like, it is common to arrange a plurality of articles of the same kind arranged in a line in a shelf from the front toward the back in a forward display state for the front surface of the shelf. For the reason, it is difficult for the conventional inventory system to correctly count the number of articles arranged in a shelf of an actual retail store or the like.